1. Field of the Invention
The present invention is directed to a method and apparatus for a passive solar day lighting system using sunlight transported into a structure through an optical conduit. More particularly, the present invention is directed to a passive lighting system that does not require active tracking of the sun and utilizes non-imaging optical collectors for concentrating collected sunlight and optical fibers for transporting light to a light fixture in a room.
2. Description of Prior Art
The use of natural light in buildings can significantly reduce the energy consumption and improve the quality of life. But interior rooms cannot benefit from a window or a sky light and only rooms immediately below a roof can enjoy a skylight. There have been several efforts to capture sunlight and deliver it to remote parts of buildings using fiber optics or light pipes or optical conduits.
Many of these previous efforts used some type of active sun tracking system coupled with complicated lens and mirror systems. For example, U.S. Pat. Nos. 4,246,477; 4,297,000 and 4,409,963 disclose various sunlight collectors, containing Fresnel lens systems. The collectors are mounted on the roof of a building and actively track the sun during daylight hours.
Other systems for collecting and transporting sunlight are disclosed in U.S. Pat. Nos. 4,307,936; 4,541,414; 4,539,625; 5,548,490 and 5,709,456. These patents disclose various devices to collect sunlight without actively tracking the sun. The U.S. Pat. Nos. 4,307,936 and 4,541,414 are directed to sunlight collecting devices that use a parabolic collector to capture sunlight and a complex arrangement of lenses to concentrate the captured sunlight. The U.S. Pat. Nos. 4,539,625; 5,548,490 and 5,709,456 are directed to large stack luminescent or fluorescent sheets arranged to collect sunlight and convert that collected light into concentrated light.
Some of these approaches have used complex, delicate systems that track the sun actively. The other systems, require either complicated mirror and lens assemblies or specialized glass collectors having luminescent or fluorescent dyes therein, making the systems so expensive that they cannot be justified by the electric energy it saves.
Passive solar tracking systems are known in the prior art. These passive tracking systems generally use solar thermal energy to track the sun's path. Solar thermal powered tracking systems are described in U.S. Pat. Nos. 4,332,240; 4,262,654; 5,600,124; 4,175,391; 4,275,712; 4,306,541 and 4,476,854. In each of these patents, a parabolic trough collects solar energy and heats fluid-containing reservoirs to cause differential vaporization and shifting of fluid to rotate the apparatus. These passive tracking systems offer a cheaper means for tracking the sun, however, the size of the collectors renders them generally unsuitable for a large scale device.